Variator-assisted CVTs are known and have been primarily devised in order to replace a conventional CVT in applications where a wide spread of gear ratios are desired. To do so with a conventional CVT would mean providing a CVT which is large and heavy, which is undesirable in a vehicle. Variator-assisted CVTs work by taking a force received at the transmission input shaft from an engine and splitting that force into two paths: one which is directed to the transmission output through a summing transmission alone, and the other which is directed through the variator and the summing transmission. Variator-assisted CVTs have primarily found use in off-highway vehicles which are used in so-called “cycling applications”, where the vehicle is required to regularly move forwards and backwards. Examples of such vehicles are track-type tractors and wheel loaders.
A limitation of such transmissions is that they are comparatively large and heavy. Thus, whilst they would be useful in non-cycling applications such as for on-highway trucks and buses, they are difficult to package (i.e. scale down) for use in these other vehicles. Furthermore, they are typically more expensive and complicated than the transmissions which are already used in these on-highway applications.
It is an aim of the present invention to obviate or mitigate one or more of these disadvantages with existing variator-assisted CVTs.